1. Field of the Invention
This invention relates to solutions useful in metal finishing processes. In particular it relates to solutions containing dithionic acid and/or dithionate salts.
2. Description of the Prior Art
Known plating electrolytes include, for instance, alkaline cyanide, acidic sulfate, acidic phosphate, acidic fluoborate and acidic methanesulfonate systems. These various electrolytes are selected by industrial practitioners of metal finishing based on the relative advantages they offer for performance, quality and environmental compatibility.
The industry is constantly seeking new and improved electrolyte systems for the finishing of metal substrates which allow for favorable differentiation of plating processes relating, for instance, to electroplating speed, performance and electrodeposit quality.
Kubo, M.; Kamitamari, T.; Hotsuta, T.; Masamoto, H.; Jpn. Kokai Tokkyo Koho JP 08269727 A2, Oct. 15, 1996, assigned to Uemura Kogyo, discloses the use of an inorganic sulfur compound selected from thiosulfate, polythhionate, dithionite, sulfite and dithionate at an amount of 0.01 to 10 mmol/L as an additive in an electroless palladium coating bath containing a palladium salt, a reductant selected from H3PO2 and its salts, H3PO3 and its salts, hydroborides, and amine borane, and complexing agent selected from NH3 and amines.
Uchida, H et al, Kokai, Tokkyo Koho JP 08269726 A2 and Uchida, H et al, German Offen. DE 19639174 A1 both disclose a solution for electroless coating of nickel. The solution contains a water soluble nickel salt, a reducing agent, a complexing agent and a compound having S—S bonds, such as, thiosulfate, dithionate, dithionite, and polythionate.